DESCRIPTION: This application is founded on data showing that expression of connexin45 in cells containing connexin43 alters gap junction communication in those cells. The data suggest that Cx43 and Cx45 interact to form gap junction with unique properties. Three specific aims are proposed. First, the investigator will characterize the interaction between Cx43 and Cx45. Second, he will determine the molecular basis for such interaction mainly through a series of site-directed mutagenesis studies. Third, he will establish the possible significance of these interactions on chemical and electrical coupling.